How about a random Alt+F4? Randomly open the optical drive? Randomly change resolution? How about throwing some Alt+Tabs out there?

It would be really sweet if these devices came with a board header so you could plug them directly into the motherboard and hide them inside the case.

@ Keyboard Devil: What if this thing was packaged to look like a USB hub, and the annoyance controls were hidden? You could give it to a friend, and not have to worry about installing the device yourself. Who's going to logically deduce that a USB hub is causing intermittent errors on their computer?